The present invention relates to a method and apparatus for detecting errors such as a cutoff and the like of an ink ribbon used in thermal transfer type multicolor printers.
With the wide use of color cathode ray tubes (CRT) in the display of personal computers and CAD systems, there has been a strong need for a printer which provides multicolor hardcopies of pictures on color CRT. In order to meet such a need, there has been proposed a thermal transfer type multicolor printer in a copending U.S. patent application Ser. No. 511,630 entitled "Method of making thermal transfer type multicolor printing," filed on July 7, 1983 and assigned to the assignee of the present application.
In the prior art thermal transfer type printers including monocolor printers, there has been used, for example, a precision snap-acting switch for detecting a cutoff of an ink film which is normally in contact with the actuator of the sensitive switch. Since the ink film is thin, time is required to set it on the actuator of the switch. Furthermore, the ink film can be scratched by the actuator. In order to avoid these drawbacks, there has been used a photosensor only for the purpose of detecting a cutoff of an ink ribbon by projecting a light beam onto that ribbon. However the use of such an exclusive photosensor is disadvantageous in cost.